A wide variety of mechanisms have heretofore been available for use in controlling the liquid level in supply tanks. For example, many have taken the form of so-called "ball cocks" utilized in water closets to establish a sufficiently high water level that a satisfactory flush of the toilet can be obtained. Such ball cocks must open the inlet line during a flush so as to permit the supply of water in the tank to be replenished, and must then be capable of shutting off automatically after the supply reaches a predetermined level in the tank.
Typical modern ball cocks operate without levers and cranks and utilize what might be termed a "pilot valve" principle in which a small secondary or "pilot" valve controls opening and closing of a main valve diaphragm through the use of a pressure chamber directly overlying the diaphragm and exposed to supply line pressure. As long as the pilot valve is closed, the pressure in this chamber is operable to retain the diaphragm seated because the surface area thereof exposed to such chamber is greater than that exposed to the supply line on the opposite side of the diaphragm. However, when the pilot valve is unseated, as a result of an operating input during a flush cycle, pressure in the overhead chamber is immediately released so as to open the diaphragm and allow the entry of a new supply of water.
Examples of ball cocks operating more or less on this principle may be found in the following patents:
______________________________________ Goldtrap 3,144,875 Goldtrap 3,144,874 Schoepe, et al 3,319,913 Schoepe, et al 3,495,803 Schoepe, et al 3,428,966 Schoepe, et al 3,429,333 Schoepe, et al 3,559,675 Schoepe, et al 3,576,199 Holderith 3,049,010 Doyle 2,808,850 Layton 2,318,236 Crockett 2,608,990 Langdon 1,626,289 Richardson 2,678,058 Martinez 2,784,733 Svirsky 2,730,122 Australian Patent Spec. 153,027 Buckner 2,744,536 ______________________________________
One serious fault with ball cocks heretofore available has resided in the fact that they open the supply line to the tank too early in the flush cycle, and thus waste a surprisingly large amount of water during each flush of the tank. In other words, prior ball cocks have started bringing in new water before all of that in the tank has been depleted, and thus a certain portion of the new water is flushed along with the volume stored in the tank instead of helping to replenish the supply.
As will be apparent from the discussion which follows, the principles of the present invention are not limited for use in connection with ball cocks, but also may be employed in a number of other areas where accurate and reliable liquid level control is required. For example, large outdoor storage tanks for petroleum products require some means for refilling the tanks automatically when they have been drained to a certain level. Control systems that employ electrical devices in conjunction with level control are entirely unsuitable for this purpose in view of the danger of explosion, and thus the present invention becomes attractive because of its ability to operate totally without an external source of power and in response solely to the level conditions within the tank.
In most instances it is desirable to allow the level of such storage tanks to drop to a certain predetermined minimum before actuating the refill cycle so that the refill control mechanism is not constantly flipping off and on so as to maintain the level at some upper predetermined point. In keeping with the principles of the present invention, this type of delayed actuation of the refill cycle in response to the liquid level dropping to a considerably low point is readily obtainable.
Governmental regulations require that all liquid level controls for use in water closets be so designed that in the event of a failure in the municipal water supply line which changes the positive supply pressure to a negative suction pressure, water in the tank will not be sucked out. Several of the assemblies found in the foregoing list of patents are provided with mechanisms designed to meet this type of requirement, but for a variety of reasons, they have been less than totally satisfactory.